AM RADIO RECEIVER

Fundamentals of AM Modulation and Demodulation

'In Amplitude Modulation the transmitted signal expressed mathematically as u(t)=Ac[1+m(t)]cos(2πfct+φc)Double-Sideband part: Acm(t)cos(2πfct+φc),Carrier Component part: Accos(2πfct+φc).

It is sometimes convenient to express m(t) as
m(t)=amn(t)
where mn(t) is normalized such that its minimum value is -1. This can be done, for example, by defining mn(t)=m(t)/max|m(t)|
The scale factor a is called the modulation index.'90

Amplitude Modulator

There are several different methods for generating AM modulating signal.Since the process of modulation involves the generation of new frequency components, modulators are generally characterized as nonlinear and, or, time-variant systems.In the figure below the Square Law Fet Amplitude modulator is depicted.

Amplitude Demodulator

At the receiver part of the AM radio, we can easily observe the carrier signal and carrier signal multiplied with message signal. Therefore we can easily separate the message from the carrier signal with the help of the combination of the rectifier and the low-pass filter which are called as an envelope detector.

In this project, first of all the antenna grabs all kind of signals from air then passes to the tuner. The tuner is used to adjust the desired frequency. For medium wave AM receiver, it is between 550kHz – 1600kHz. To achieve that it is necessary to use an inductor and a capacitor. After we obtain the signal which is at desired frequency, we should amplify this signal in order to get a sufficiently large signal. To do that, we used diode and a low-pass filter as a detector. At this state we have the pure message signal. As a next step we should amplify the signal again and again to he ar the audio signal from speaker more easily.

Tuner Design

LC resonant circuit comprising L1 and VC1 used to select or tune the required frequency and station. L1 is a coil of wire wound on a ferrite rod. 
This behaves like a transformer - currents flowing in L2 generate a changing magnetic flux which cuts L1 and induces an emf in it.

The Antenna Graps All Kind of Signals from the Air